"It is the greatest spectacle in racing. The Indianapolis 500, if you win that, you absolutely have done it," said Unser.

No one has won the Indianapolis 500 more than Unser, who took the checked flag on four separate occasions.

"I should have won it 10 times, but there were too many other guys. All race drivers have one thing in common. They are going to try and win that race that day regardless of what it takes, you just can't imagine what it's like to go against those kinds of odds," Unser said.

Unser's brother, Bobby, won the Indy 500 three times. Unser said running against his son, Al Unser Jr., was even tougher.

"I found out it was a lot harder running against your son than it is your brother," Unser said. "It tore me up for a while. I finally got used to it, but every time there was a caution flag or somebody crashed, I always pushed that button and I'd say, 'Is Al OK?'"

Unser is the all-time lap leader and the oldest person tow in the Indy 500 at 47 years old.